linux-kernel - Re: [PATCH] checkpatch: prefer = {} initializations to = {0}

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Message-ID: <a427b32e-f513-f1ed-5b28-581326f22ad4@wanadoo.fr>
Date:   Sat, 14 Aug 2021 16:05:46 +0200
From:   Marion & Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Leon Romanovsky <leon@...nel.org>
Cc:     Joe Perches <joe@...ches.com>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Andy Whitcroft <apw@...onical.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Julia Lawall <julia.lawall@...ia.fr>
Subject: Re: [PATCH] checkpatch: prefer = {} initializations to = {0}

Copy paste error, see below :/

Le 14/08/2021 à 15:59, Christophe JAILLET a écrit :
> Hi all,
> 
> Le 05/08/2021 à 12:43, Dan Carpenter a écrit :
>> The "= {};" style empty struct initializer is preferred over = {0}.
>> It avoids the situation where the first struct member is a pointer and
>> that generates a Sparse warning about assigning using zero instead of
>> NULL.  Also it's just nicer to look at.
>>
>> Some people complain that {} is less portable but the kernel has
>> different portability requirements from userspace so this is not a
>> issue that we care about.
>>
>> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
>> ---
>>   scripts/checkpatch.pl | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
>> index 461d4221e4a4..32c8a0ca6fd0 100755
>> --- a/scripts/checkpatch.pl
>> +++ b/scripts/checkpatch.pl
>> @@ -4029,6 +4029,12 @@ sub process {
>>                    "Using $1 is unnecessary\n" . $herecurr);
>>           }
>> +# prefer = {}; to = {0};
>> +        if ($line =~ /= \{ *0 *\}/) {
>> +            WARN("ZERO_INITIALIZER",
>> +                 "= {} is preferred over = {0}\n" . $herecurr);
>> +        }
>> +
>>   # Check for potential 'bare' types
>>           my ($stat, $cond, $line_nr_next, $remain_next, $off_next,
>>               $realline_next);
>>
> 
> [1] and [2] state that {} and {0} don't have the same effect. So if 
> correct, this is not only a matter of style.
> 
> When testing with gcc 10.3.0, I arrived at the conclusion that both {} 
> and {0} HAVE the same behavior (i.e the whole structure and included 
> structures are completely zeroed) and I don't have a C standard to check 
> what the rules are.
> gcc online doc didn't help me either.
> 
> To test, I wrote a trivial C program, compiled it with gcc -S and looked 
> at the assembly files.
> 
> 
> Maybe, if it is an undefined behavior, other compilers behave 
> differently than gcc.
> 
> 
> However, the 2 persons listed bellow have a much better Linux and C 
> background than me. So it is likely that my testings were too naive.
> 
> 
> Can someone provide some rational or compiler output that confirms that 
> {} and {0} are not the same?
> 
> Because if confirmed, I guess that there is some clean-up work to do all 
> over the code, not only to please Sparse!
> 
> 
> Thanks in advance.
> CJ
> 
> 
> 
> [1]: Russell King - 
> https://lore.kernel.org/netdev/YRFGxxkNyJDxoGWu@shredder/T/#efe1b6c7862b7ca9588c2734f04be5ef94e03d446 
> 
> 
> [2]: Leon Romanovsky - 
> https://lore.kernel.org/netdev/YRFGxxkNyJDxoGWu@shredder/T/#efe1b6c7862b7ca9588c2734f04be5ef94e03d446 
https://lore.kernel.org/netdev/162894660670.3097.4150652110351873021.git-patchwork-notify@kernel.org/T/#m3424d6e97ef0f0ddd429cce3369a6da0ea9af276